Influence of shrub willow buffers strategically integrated in an Illinois corn-soybean field on soil health and microbial community composition.

Soil serves many important ecological functions and is an integral part of our existence as a society. However, concerns for soil health are growing globally, in part due to the negative impacts of agricultural management on soil resources. The production of perennial bioenergy crops on marginal land in row-crop production systems is one solution that could improve land-use efficiency and address the sustainability of cropland management. Because the relationship between crop management and the environment is complex, more research is needed to evaluate the potential benefits perennial bioenergy crop production has on soil health, as well as other ecosystem services. In this study, shrub willow buffers were strategically integrated into a corn-soybean cropping system with the main objective of reducing nitrate-N leaching from grain crop production while producing biomass for bioenergy. Two buffer systems (defined by landscape positions) were included for comparison, one on marginal land with exposure to nitrate-N leaching from upslope grain (southern plots) and one on fertile soils with less nitrate-N leaching potential (northern plots). Evaluation of soil (chemistry, bulk density, microbial community) and shrub willow vegetation properties (fine roots, leaf litter decomposition, and nutrient uptake dynamics), showed that landscape position plays an important role in (1) the dynamics of soil chemical properties, (2) shrub willow's influence and productivity, and (3) the provision of additional ecosystem services such as reductions in nitrous oxide emissions and nitrate-N leaching. In addition, the combination of crop type and landscape position (N-grain, N-willow, S-grain, and S-willow) influenced the species composition of the soil microbial community, resulting in unique and identifiable communities. These results highlight the potential application of shrub willow buffers for ecosystem service provision and support of ecosystem processes; however, understanding the relationship between the microbial community, crop type, and landscape is important for understanding the sustainability of the design.

Differential Functional Constraints Cause Strain-Level Endemism in Polynucleobacter Populations.

The adaptation of bacterial lineages to local environmental conditions creates the potential for broader genotypic diversity within a species, which can enable a species to dominate across ecological gradients because of niche flexibility. The genus Polynucleobacter maintains both free-living and symbiotic ecotypes and maintains an apparently ubiquitous distribution in freshwater ecosystems. Subspecies-level resolution supplemented with metagenome-derived genotype analysis revealed that differential functional constraints, not geographic distance, produce and maintain strain-level genetic conservation in Polynucleobacter populations across three geographically proximal riverine environments. Genes associated with cofactor biosynthesis and one-carbon metabolism showed habitat specificity, and protein-coding genes of unknown function and membrane transport proteins were under positive selection across each habitat. Characterized by different median ratios of nonsynonymous to synonymous evolutionary changes (dN/dS ratios) and a limited but statistically significant negative correlation between the dN/dS ratio and codon usage bias between habitats, the free-living and core genotypes were observed to be evolving under strong purifying selection pressure. Highlighting the potential role of genetic adaptation to the local environment, the two-component system protein-coding genes were highly stable (dN/dS ratio, < 0.03). These results suggest that despite the impact of the habitat on genetic diversity, and hence niche partition, strong environmental selection pressure maintains a conserved core genome for Polynucleobacter populations. IMPORTANCE Understanding the biological factors influencing habitat-wide genetic endemism is important for explaining observed biogeographic patterns. Polynucleobacter is a genus of bacteria that seems to have found a way to colonize myriad freshwater ecosystems and by doing so has become one of the most abundant bacteria in these environments. We sequenced metagenomes from locations across the Chicago River system and assembled Polynucleobacter genomes from different sites and compared how the nucleotide composition, gene codon usage, and the ratio of synonymous (codes for the same amino acid) to nonsynonymous (codes for a different amino acid) mutations varied across these population genomes at each site. The environmental pressures at each site drove purifying selection for functional traits that maintained a streamlined core genome across the Chicago River Polynucleobacter population while allowing for site-specific genomic adaptation. These adaptations enable Polynucleobacter to become dominant across different riverine environmental gradients.

An Integrated Landscape Designed for Commodity and Bioenergy Crops for a Tile-Drained Agricultural Watershed.

Locating bioenergy crops on strategically selected subfield areas of marginal interest for commodity agriculture can increase environmental sustainability. Location and choice of bioenergy crops should improve environmental benefits with minimal disruption of current food production systems. We identified subfield soils of a tile-drained agricultural watershed as marginal if they had areas of low crop productivity index (CPI), were susceptible to nitrate-nitrogen (NO-N) leaching, or were susceptible to at least two other forms of environmental degradation (marginal areas). In the test watershed (Indian Creek watershed, IL) with annual precipitation of 852 mm, 3% of soils were CPI areas and 22% were marginal areas. The Soil and Water Assessment Tool was used to forecast the impact of growing switchgrass ( L.), willow ( spp.), and big bluestem ( Vitman) in these subfield areas on annual grain yields, NO-N and sediment exports, and water yield. Simulated conversion of CPI areas from current land use to bioenergy crops had no significant ( 0.05) impact on grain production and reduced NO-N and sediment exports by 5.0 to 6.0% and 3.0%, respectively. Conversion of marginal areas from current land use to switchgrass forecasted the production of 34,000 t of biomass and reductions in NO-N (26.0%) and sediment (33.0%) exports. Alternatively, conversion of marginal areas from current land use to willow forecasted similar reductions as switchgrass for sediment but significantly ( 0.01) lower reductions in annual NO-N export (18.0 vs. 26.0%).

Achieving the Great Lakes Initiative mercury limits in oil refinery effluent.

To meet the stringent Great Lakes Initiative (GLI) wastewater discharge mercury (Hg) limit of 1.3 ppt (ng/L), mercury removal technologies need to be identified and investigated. The goals of this study were to (1) identify and assess available wastewater treatment technologies for mercury removal from an oil refinery wastewater; and (2) conduct bench-scale tests to provide comparable, transparent, and uniform results to assess their performance at low mercury concentrations. The study found that many tested technologies were able to achieve the GLI mercury target concentration at the bench-scale, albeit with different efficiencies and engineering implications. These results demonstrate that at this scale there is no fundamental physical or chemical barrier to achieving < 1.3 ng Hg/L in the tested wastewater. The study also found that some technologies were effective on particulate mercury whereas others were effective on dissolved mercury. One emerging treatment technology was found to be effective on both particulate and dissolved mercury. Three mercury-removal technologies--ultrafiltration (particulate mercury), adsorption (dissolved mercury), and an emerging reactive filtration technology (particulate and dissolved mercury)--are recommended for further study. This research offers treatment alternatives for different forms of mercury in an oil refinery wastewater, which might be applicable to other types of mercury-containing wastewater.

Meeting world's most stringent Hg criterion: a pilot-study for the treatment of oil refinery wastewater using an ultrafiltration membrane process.

A membrane ultrafiltration (UF) technology was tested using an oil refinery's end-of-pipe effluent to demonstrate the proof of concept, i.e. can the Great Lakes Initiative criterion of less than 1.3 ppt be consistently met at the pilot-scale, and to provide the data necessary for preliminary full-scale process design. This study presents the successful pilot test conducted with continuous but varying feed conditions over a protracted period. The UF membrane process consistently provided a constant permeate quality at all tested operating conditions, virtually independent of the feed water characteristics and the feed Hg concentration (0.5-22.7 ppt). The treatment target of less than 1.3 ppt of Hg was met and exceeded for all tested conditions during the pilot study. Turbidity measurements were <0.5 NTU (with a MDL of 0.5 NTU) 85% of the time and <0.16 NTU 95% of the time when analyzed on-line. The TMP values were below the specification of (negative) 7-12 psi at all tested conditions during the pilot-study. Weekly maintenance cleans and monthly clean in place (CIP) events were very effective in consistently restoring the membrane permeability during the pilot-study.

Achieving very low mercury levels in refinery wastewater by membrane filtration.

Microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) membranes were evaluated for their ability to achieve the world's most stringent Hg discharge criterion (<1.3ng/L) in an oil refinery's wastewater. The membrane processes were operated at three different pressures to demonstrate the potential for each membrane technology to achieve the targeted effluent mercury concentrations. The presence of mercury in the particulate form in the refinery wastewater makes the use of MF and UF membrane technologies more attractive in achieving very low mercury levels in the treated wastewater. Both NF and RO were also able to meet the target mercury concentration at lower operating pressures (20.7bar). However, higher operating pressures (≥34.5bar) had a significant effect on NF and RO flux and fouling rates, as well as on permeate quality. SEM images of the membranes showed that pore blockage and narrowing were the dominant fouling mechanisms for the MF membrane while surface coverage was the dominant fouling mechanism for the other membranes. The correlation between mercury concentration and particle size distribution was also investigated to understand mercury removal mechanisms by membrane filtration. The mean particle diameter decreased with filtration from 1.1±0.0µm to 0.74±0.2µm after UF.

Improving data quality on low level mercury wastewater analysis.

In order to compare treatability test results evaluating low-level mercury (Hg) removal from oil refinery wastewater, improvements in Hg analytical methods were conducted at two US EPA certified analytical labs. The revisions in the analytical protocols improved Hg recoveries and hence enabled more reliable data interpretation and comparison for the specific wastewater tested. Nevertheless, significant differences between results from the two laboratories were identified in a split-sample experiment.

Biofuels, land, and water: a systems approach to sustainability.

There is a strong societal need to evaluate and understand the sustainability of biofuels, especially because of the significant increases in production mandated by many countries, including the United States. Sustainability will be a strong factor in the regulatory environment and investments in biofuels. Biomass feedstock production is an important contributor to environmental, social, and economic impacts from biofuels. This study presents a systems approach where the agricultural, energy, and environmental sectors are considered as components of a single system, and environmental liabilities are used as recoverable resources for biomass feedstock production. We focus on efficient use of land and water resources. We conducted a spatial analysis evaluating marginal land and degraded water resources to improve feedstock productivity with concomitant environmental restoration for the state of Nebraska. Results indicate that utilizing marginal land resources such as riparian and roadway buffer strips, brownfield sites, and marginal agricultural land could produce enough feedstocks to meet a maximum of 22% of the energy requirements of the state compared to the current supply of 2%. Degraded water resources such as nitrate-contaminated groundwater and wastewater were evaluated as sources of nutrients and water to improve feedstock productivity. Spatial overlap between degraded water and marginal land resources was found to be as high as 96% and could maintain sustainable feedstock production on marginal lands. Other benefits of implementing this strategy include feedstock intensification to decrease biomass transportation costs, restoration of contaminated water resources, and mitigation of greenhouse gas emissions.